Process for the recovery of platinum



Aug. 11, 1953 H. HOLZMANN 2,648,393

PROCESS FOR THE RECOVERY OFA PLATINUM Filed Feb. l, 1950 INVENTOR/f/v/QAM//Voz z/V/y/v/V,

www?l Maf/d? ATTORNEYS Patented Aug. l1, 1953 .zg OFFICE PROCESS FOR THERECOVERY OF PLATINUM Hermann Holzmann, Hanau (Main), Germany,

assignor to Deutsche Goldund Silber- Scheideanstalt, vormals Roessler,Frankfurt am Main, Germany, a corporation of Germany Applicationliiebruary 1, 1950, Serial No. 141,700 In Switzerland February 3, 1949 5Claims. l

My invention relates to an improvement in the process for the recoveryof platinum lost from precious metal catalysts such as they are used inmethods of reacting gas mixtures by means of a precious metal catalyst.

The principal object of my invention is to recover the platinum which isused in catalytic processes, as for instance, the oxidation of ammoniaand the like, whereby the platinum shows a distinct tendency tovolatilize. This is accomplished according to this invention byinserting battles in the gas iiow behind the catalyst at a place with asufficiently high temperature to bind the volatile platinum, whereby thebaffles consist as a whole or partly, or at least in part of theirsurface of metal oxides. Practically no obstruc tion to the gas flow isexerted by the bailles.

It is an object of this invention to utilize baffles in the form ofnetworks, said networks being coated with a thin layer of a noble metal.

it is a further object of this invention to fabricate networks oi alloysof noble metals with base metals as baffles for the recovery ofplatinum.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being made to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In catalytic reactions, as for instance, in the oxidation of ammonia tonitrogen oxides, carried out at temperatures of about 800c C. by meansoi platinum catalysts in form of networks or foils, a permanent loss ofsubstantial quantities of platinum is involved, i. e. a loss oi" 6.3 g.of platinum per ton of reacted nitrogen. Evidently these P.

losses are caused by the strong disintegration of the platinum structurewhich results in the formation of platinum black.

According to my observations it must be assumed that the `platinum iscontained in the gas flow in three different forms, i. e. in the form oiplatinum vapor, in the form of solid platinum particles, formed by theconversion into `platinum black, and in the form oi platinum oxideparticles.

By inserting` a mechanically acting filter, for instance, quartz wool,glass wool or metal wool, about one half of the platinum, substantiallyin the form of solid platinum particles may be retained. This mechanicalfiltering action has the disadvantage that a considerable fall ofpressure occurs, which causes a decrease in the reacted quantity oiammonia.

The capability of gold to trap platinum particles at higher temperaturesby welding at the point of contact, enables the construction of devicesor collecting the very nely subdivided platinum particles carriedforward with the gas flow whereby no mechanical lter is necessary.Instead of these mechanical Jfilters, baies with a thin coating of goldmay be utilized. These bai,- es may be given `a shape which allows apractically unchecked gas flow. In the hitherto known processes thesebales are mainly developed in the form of nlling bodies, as forinstance, porcelain rings (so-called Raschig rings) which are insertedin a thick layer immediately behind the platinum catalyst. The iillingbodies are coated with a very thin layer of gold. At the prevailing hightemperature the platinum particles which impinge on the Raschig ringsserving as baffles immediately adhere to the gold surface. Thus it waspossible to recover up to 70 percent of the lost platinum without anyharmful fall of pressure. The reason why not all the lost platinum maybe recovered lies in the fact that the platinum in its oxide form passesthe baies more or less freely.

It has now been found that according to the same principle as carriedout in the recovery of the metallic parts by gold without the use of amechanical filter it is possible to collect also the platinum in form ofoxide. At a sufficiently high temperature the platinum oxide particlesare trapped by the baffle plates with an oxide surface, obviously in thesame manner as the metallic particles of platinum are welded with themetallic blank gold immediately after the impact. It is highly probablethat the platinum oxide is collected by the base metal oxides in a solidsolution or that the platinum undergoes a chemical com bination.

Particularly favorable results were obtained with baliles in form ofnetworks and mixtures oi nickel oxides, chromium oxides and manganeseoxides. Iron oxides have also proved effective. Expediently, thenetworks are fabricated from metals or alloys which are sufficientlystable at the physical and chemical conditions prevailing in vthe gasphase behind the platinum catalyst. rihese networks serve at the sametime as support for the oxide mixtures.

Comparative experiments between gold networks and networks consisting inan alloy of the following composition (known as electric resist antmaterial) Per cent Nickel 74.5 Chromium 20.0 Manganese 35 Silicium 1.5

Thorium 1 0.5

with an oxide layer formed by annealing the alloy under workingconditions or before the installation, gave the following results:

Thereby the networks are spaced with 15 mm., the first network beingarranged at a distance of 50 cm. from the platinum catalyst. The networkcontained 3.600 meshes per sq. cm., wire gage 0.070 mm. A distinctsuperiority in the use of gold over the base metal alloy could bebserved. The six metal networks were able to accumulate a total amountof 79.34 percent of the platinum if gold was employed, and 70.60 percentif base metals with an oxide layer were used. The conception that thepure metallic surface cannot retain any oxide particles nor the oxidesurface any metallic particles of the platinum, i. e. that the recoveryof platinum at the gold networks, and at the base metal networks wouldtotal at least 100 percent, has proved deceptive. In both theseexperiments, however, a recovery of 150 percent was obtained. This factleads to the assumption that the gold network also retains a certainamount of the platinum oxide and that the base metal network alsoretains a certain amount of the metallic platinum. This can easily bedeclared by the fact that particles of platinum metal and platinum oxideare not distinctly separated but that there exist also particles whichare composed both of platinum metal and platinum oxide. Further, theoxide layer on the base metal network is not always coherent, andtherefore leads to a pure metal effect of the network surface althoughto a lesser degree.

It has now been found that by a combined use of metal and oxide baillesit is possible to practically recover the whole platinum carried in thegas flow. The particular combination may be carried out in numerousconstructions. Thus, for instance, the networks with a gold surface andthose with an oxide surface may be arranged alternately in a seriesconnection. It has been found to be particularly advantageous if boththese different net types are combined in one single network whereby itis of no consequence whether the wires with a gold surface are used asweft and those with an oxide surface are used as warp or vice versa.

The utilization of the baffles in form of networks has the furtherdistinct advantage that the single network may be employed for a ratherlong time, i. e. until its saturation with platinum is completed. Thisis accomplished by interchanging the networks after a period of sixmonths, for instance, by dismantling the network situated next to theplatinum catalyst and adding a new network at the opposite side of theplatinum catalyst. Therefore it is only necessary to dismantle thenetwork which is completely saturated with platinum.

Referring to the annexed drawings:

Fig. 1 shows a top view b of a baffle in the form of a network accordingto the invention, and; Fig. 2 shows a side View a of a series of sixsuperposed networks. Fig. 3 shows a top view c of a baille in the formof a plurality of associated strips or foils, and; Fig. 4 shows a sideview d of a series of baffles formed of a plurality of strips or foils.

The use of baiiles having oxide and noble metal coatings in the form ofnetworks is preferable in view of their ease of installation, simplicityof construction and gas permeability. However.. other forms of bales,for example, in the form of foils or strips such as shown in Figs. 3 and4 can also be employed. Preferably the individual baffles in the seriesof baffles are staggered with respect to each other so that the gaseswhich pass through the openings in one baille will tend to impinge uponthe surface of the next baffle. At points in the apparatus where thegases are caused to change their direction of flow, inclined baiiles ofsimple construction can be inserted with advantage if the temperaturesof the gases are sufliciently high at these points.

Networks which are only made of gold need a considerable investment ofgold. Furthermore, they show an inferior stability at the occurringtemperatures of about 700 C. More favorable are base metal networks withsuitable heat resistant and non-scaling alloys which are coated with agold layer. In this case, however, it is necessary to avoid thediffusion of the gold layer into the metallic support. According to myinvention it is now possible to prevent such a diffusion in differentways. At first, an oxide layer on a network made of a chromium nickelalloy is produced by annealing at the open air. This oxide layer is thencoated by a thin gold layer, either by cathodic atomization or bythermal evaporation in vacuo or by burning up of a socalled organicbright gold solution. Subsequently, the very thin coating thus formedmay be reinforced by galvanization. The oxide layer between core andcover practically hinders the diffusion of the gold layer into the core.

A further embodiment of my invention resides in inserting a layerbetween the gold layer and the base metal core, said layer consisting ina metal which does not alloy with the support metal no1` with the goldlayer. Such a multilayer wire may, for instance, have the followingcomposition:

Core Nickel 1. Intermediate layer Silver 2. Intermediate layer RhodiumCoating Gold The silver does not react with nickel or with rhodium, northe rhodium with silver or gold. Hence it follows that the gold coverremains unchanged at the respective working temperature. In proportionas the platinum accumulates on the gold and alloys with the gold, amixture of the different layers takes place because the platinum formsmixed crystals with all components. Nevertheless, the surface of themetal always remains blank.

In the same manner as gold other noble metals, particularly silver havebeen found to be suited as a platinum trap. The use of silver, however,meets with difficulties because of its tendency to recrystallization andgrain growth in connection with its property to dissolve oxygen.Networks made from fine silver fall to powder when used.

Thin silver coatings, however, on the support of another metal whichdoes not form an alloy with silver like nickel Vor chromium-nickel, arestable. If desired, also a block layer, for instance,

6 parting from thespirit and scopethereof, itisto be understood that Ido not limit myself to .the specific embodiments 'thereof except fasdefined in the appended patent'claims.

an oxide layer may be used. In this case other 5 I- claim SlllJlOOrtmetals may be employed. It has been -1. A method for collecting`platinum contained found to be even more advantageous to use silver ina highly heated gas stream leaving a'platinum allOyS instead Of Silver,fOr irlStaIlCe, allOYS Of catalyst which comprises passing such gasesover Silver With sold, palladium 01 platinum, either bales exertingsubstantially noobstructionto the alone or in combination with eachother. Excel- 1o flow of thegas stream, and having a core comlent yieldswere obtained with networks consistprising at least one metal having anatomic numing in wires with a nickel core and a coating made ber from 241-,0 23, indusive, and having a, surface 0f an allOy With 80 pereelt OSilver and 20 per comprising at least one metal oxide of a metal cent ofgold as summarized belOW having an atomic number from 24 to 29,inclusive,

TABLE II and over baiiles exerting substantially no obstruction to theflow of the gas stream, and having a Recoym Percentage core comprisingat least one metal having an Per Cent atomic number from 24 to 28,inclusive, and hav- Network No. 1 5790 ing a surface comprising at leastone noble metal Network No, 2 11,26 20 of the group consisting ofpalladium, platinum, Network No. 3 2.64 gold and silver. Network No. 41.70 2. A method for collecting platinum contained Network No. 5 0.88 ina highly heated gas stream leaving a platinum Network No. 6 0.76catalyst which comprises passing such gases over bales exertingsubstantially no obstruction to 'i5-14 the ow of the gas stream, andhaving a core Surprisingly, the nickel core was completely comprising atleast one metal having an atomic transformed into nickel oxide duringthe duranumber from 24 t0 28, iIlClllSive. and having a tion of test,Consequently, the Oxygen diffused surface comprising at least one met-aloxide of a through the silver-gold layer right into the core. metalhaving an atomic number from 24 to 29, Non-scaling base metal alloys areparticularly inclusive, and over baiiies exerting substantially Suitedt0 the DllrDOSe alSO irl COImeCtiOrl With no obstruction to the flow ofthe gas stream, and silver alloys as described. The following alloyshaving a, Core Comprising at least one metal havwhich are non-scalingand resistant against aning .an atomic number from 24 to 28, inclusive,nealing, may serve as supports with or without a and having a Surfacecomprising gold. Coatmg 0f a' noble metal: 3. A method for collectingplatinum contained TABLE lI in a highlyheated gas stream leaving aplatinum Chromiui2r/i215ickel steel Resistance alloy `Chromiurignickelsteel Iron, 5l percent Iron, 64.5 percent Iron, 74 percent.

Nickel, 26 percent Chromium, 30 pe1cent Chromium, 18 percent.

Chromium, 20 percent Aluminum, 5 percent Nickel, 8 percent.

Manganese, 2 peroent Thorium, 0.5 percent Silicium, l percent It is evenpossible to catch platinum metal catalyst which comprises passing suchgases over particles and platinum OXide particles by baes 5o bafllesexerting substantially no obstruction to the which do not consistentirely of oxides or of a 30W of the gas Stream, and having a, corecomblanlr noble metal or Whieh d0 not have a Te' prising at least onemetal having an atomic numspective coherent oxlde layer. Ontthesesurfaceles ber from 24 to 23, inclusive, and having a surface the metaleIleCt 31rd the OXlde effec Occurs Sm@ comprising at least one metaloxide of a metal taneously. r'or this purpose alloys of silver wlth 55havin at b f 24 copper or another base metal have been found g an 0mmmlm er Tom t0.291nCll1S1ve, to be advantageous. and O Ver J bafflesexertm' Substantially n0 ob- The deposit may also be increased if thebaffle, tfuctlon U0 the 110W 0f the eas Stream, and havfor instance, thenetwork, is electrostatically mg a Core COmDI'lSlIlg at leaSt 011e metalhaving Charged or earthed, as it has been found that the an atomicnumber from 24 to 28, inclusive, and yield in the recovered platinum maybe further having a Surface COrlDliSillg Silver. improved by the action.4. A method for collecting platinum contained It is desirable to placethe baiiies directly in the in a highly heated gas stream leaving aplatinum reaction chamber in order to catch most of the catalyst whichcomprises passing such gases over catalyst meta-l. baiiles exertingsubstantially no obstruction to While I have described my invention inpartcuthe flow of the gas stream, and having a core comlar referenee t0tlleOXCietOl of ammOIa to 9X prising at least one metal having an atomicnumprlllgelhtrygl IIISIO ber from 24 to 28, inclusive, and having asurface platinum metal catalysts used in the reacting of Compnsmg atleast one metal Oxlde of a metal other gas mixtures and the conversionof gases other than ammonia provided the platinum catalyst is operatedat elevated temperatures.

lAs many apparently widely different embodiments of my invention may bemade without dehaving an atomic number from 24 to 29, inclusive, andover baffles exerting substantially no obstruction to the flow of thegas stream, and having a core comprising at least one metal having anatomic number from 24 to 28, inclusive,

and having a surface comprising gold and silver alloy, References Citedin the le of this patent 5. A method OI Collecting platinum ContainedUNITED STATES PATENTS in a highly heated gas stream leaving a platinumcatalyst which comprises passing such gases over 5 Number Name Datebailles exerting substantially no obstruction to 2226'113 Chastam Dec 241940 the iloW of the gas stream, and having a core 2226149 ZimmermannDec 24 1940 comprising at least one metal having an atomic number from24 to 28, inclusive, and having a ,i surface comprising silver andcopper oxide. 10 l HERMANN HOLZMANN.

1. A METHOD FOR COLLECTING PLATINUM CONTAINED IN A HIGHLY HEATED GASSTREAM LEAVING A PLATINUM CATALYST WHICH COMPRISES PASSING SUCH GASESOVER BAFFLES EXERTING SUBSTANTIALLY NO OBSTRUCTION TO THE FLOW OF THEGAS STREAM, AND HAVING A CORE COMPRISING AT LEAST ONE METAL HAVING ANATOMIC NUMBER FROM 24 TO 28, INCLUSIVE, AND HAVING A SURFACE COMPRISINGAT LEAST ONE METAL OXIDE OF A METAL HAVING AN ATOMIC NUMBER FROM 24 TO29, INCLUSIVE, AND OVER BAFFLES EXERTING SUBSTANTIALLY NO OBSTRUCTION TOTHE FLOW OF THE GAS STREAM, AND HAVING A CORE COMPRISING AT LEAST ONEMETAL HAVING AN ATOMIC NUMBER FROM 24 TO 28, INCLUSIVE, AND HAVING ASURFACE COMPRISING AT LEAST ONE NOBLE METAL OF THE GROUP CONSISTING OFPALLADIUM, PLATINUM, GOLD AND SILVER.
 5. A METHOD FOR COLLECTINGPLATINUM CONTAINED IN A HIGHLY HEATED GAS STREAM LEAVING A PLATINUMCATALYST WHICH COMPRISES PASSING SUCH GASES OVER BAFFLES EXERTINGSUBSTANTIALLY NO OBSTRUCTION TO THE FLOW OF THE GAS STREAM, AND HAVING ACORE COMPRISING AT LEAST ONE METAL HAVING AN ATOMIC NUMBER FROM 24 TO28, INCLUSIVE, AND HAVING A SURFACE COMPRISING SILVER AND COPPER OXIDE.